This invention relates to a module board and an electronic device having a plurality of semiconductor devices mounted on the module board.
The memory board of a computer has a mother board including connection patterns and so on and a plurality of memory modules mounted thereon in order to construct one memory system. This memory board tends to increase its capacity, and hence, the number of semiconductor memory devices to be mounted per unit area of the module board of each memory module (namely, the packing density tends to be increased). On the memory board are mounted a plurality of electronic devices (memory modules), each of which, as shown in FIG. 1A (plan view) and FIG. 2 (side view), has a plurality of semiconductor memory devices 2 mounted on the main surface including wiring patterns (hereinafter, referred to as the mounting surface) of a board (module board) 1, and lead pins 3 provided along one edge of this module board 1 to electrically connect to the semiconductor devices 2. These electronic modules, or devices are mounted on the mounting surface of the memory board 100 so that the module boards 1 are vertically erected on the mounting surface as shown in FIG. 1B. Thus, the way to mount these electronic modules on the mounting surface of the memory board 100 can increase the packing density since the area which the modules occupy on the mounting surface is small.
The module board 1 is made of, for example, an epoxy-based resin printed-module board having wiring conductor pattern provided on the surface or within it. This printed wiring pattern is formed of a single-layer or multilayer, and electrically connects the semiconductor memory devices 2 and the lead pins 3.
The semiconductor memory device 2 is, for example, a DRAM (Dynamic Random Access Memory). This semiconductor memory device 2 has a semiconductor chip with a DRAM function packaged by plastic molding. The plastic mold package is, for example, in a SOJ type or DIP type structure.
The lead pins 3 each have first end formed in a clamp shape as shown in FIGS. 2 and 3 (perspective views). The first end of each lead pin 3 holds between its tongues a margin 1A at one edge of the module board 1 and is bonded and fixed thereto with solder 4. Thus, the first ends (clamp portions) of the leads 3 are electrically connected to the wiring conductors of the module board 1 by the bonding using the solder 4. The other (second) ends of the lead pins 3 are inserted into the mounting surface of the memory board (mother board). In other words, the electronic modules are mechanically and electrically connected to the wiring conductors of the module board 1 through the lead pins 3 and mounted on the mounting surface of the memory board (mother board) since the connection of the first ends of the lead pins 3 to the margins is mechanically strengthened with their clamping force (elastic force).
Lead pin insertion type electronic modules are described, for example, in the Hitachi IC MEMORY DATA BOOK, Mar. 1989., pp. 697-708.
In this electronic module, however, the module board 1 has the margin 1A which first ends of the lead pins 3 hold between their tongues as described above. This margin 1A assures a mechanical strength and makes electrical connection, but occupies a large area on the mounting surface of the module board 1. Thus, since the area of the module board 1 is increased by the amount corresponding to the area occupied by the margin, the packing density of the electronic module is reduced.
Moreover, in the memory board on which the electronic modules are mounted, the height of the vertically mounted modules relative to the mounting surface is increased by the amount corresponding to the area of the margin 1A provided on the module board 1, and thus the packing density in the height direction is reduced.
In addition, the lead pins 3 of the module are bonded to the margin with the solder 4 which has a low melting point, and a great number of semiconductor memory devices 2 are mounted at a high density on the module board. Therefore, the solder 4 may be melted by heat generated by the semiconductor memory devices 2. In this case, the module board 1 of the electronic module would be supported by only the clamping force of the lead pins 3. Thus, the resulting poor bonding between the lead pins 3 and the module board 1 will reduce the electrical reliability of the module.
Also, each of the lead pins 3 of the module, as shown in FIG. 3, has three clamping tongues provided on its first end, one of which holds the mounting surface of the module board and the other two of which hold the opposite surface thereof, thereby clamping the margin of the module board. Therefore, the arrangement pitch of the lead pins 3 along the margin is determined by the two clamping tongues at one end of each lead pin, so that the area occupied by the margin 1A is increased in the arrangement direction of the lead pins 3 along the edge of the module board 1, thus lowering the packing density of the module.
In this connection, JP-U-63-75051 (Japanese Utility Model Application Laid-open No. 63-75051, laid open on May 19, 1988) discloses a semiconductor module mounted on a printed circuit board with its lead pins similar to those shown in FIG. 3 inserted into through holes.